There are known cables such as an overhead electricity line described in EP No. 286 804, having a steel wire core with a number of steel wires stranded around the core wire and where one of the outer wires is substituted with a steel tubule containing a number of optical fibers. A layer of aluminium wires are stranded around core wires to make up the overhead line. Such a construction is, however, for a number of reasons not suitable for use in oil wells.